Xerostomia is a condition in which the salivary glands do not produce sufficient quantities of saliva. This causes discomfort which can in some cases be quite severe. Without saliva, the mouth burns and the throat and tongue can undergo radical changes. Teeth can decay rapidly and the tongue can become smooth, cracked and vulnerable to infection. There is often a loss of taste and, because saliva contains important digestive enzymes, there are often problems with digestion.
The mouth is one of the body areas most exposed to the external environment. Normally, mucous forms a continuous protective layer in the nose, mouth and throat. A patient suffering from xerostomia not only has decreased fluid in the mouth, but also an insufficient quantity of mucoproteins and mucopolysaccharides to hold fluid in contact with the cells and create a barrier to irritation and infection.
It is estimated that several million individuals suffer from this condition nationwide. The actual number of individuals suffering from xerostomia is not known, however, because until recently there has been little acknowledgement of the prevalence or severity of the problem.
Cases of xerostomia may vary from the mild, in which only slight dryness is experienced, to severe cases in which the patient will have serious problems with mastication, swallowing, digestion, speech, and the like. As noted in U.S. Pat. No. 4,438,100 to Balslev et al., there are a number of causes of xerostomia, including the physiological (e.g., age, menopause, postoperative conditions, dehydration), as well as the psychic (nervousness). The reasons for mouth dryness may also be pharmacological (e.g., as a common side effect of many medications, including diuretics, anti-arthritics and anti-depressants) or as a result of radiotherapy. The most severe cases of xerostomia are caused by radiation therapy after head and neck surgery and by autoimmune diseases such as lupus, Sjogrens Syndrome, and rheumatoid arthritis. See, for example, P.C. Fox et al., J. Am. Dental Assoc. 110:519-525 (1985).
Until recently, the treatments for xerostomia have had significant drawbacks. For example, symptoms of mild xerostomia can be somewhat alleviated by consumption of fluids, hard candy and throat lozenges. Because of the susceptibility of xerostomia patients to tooth decay and gum disease, however, the increased sugar intake associated with conventional candy and lozenges is of real concern. In addition, fluids or candy are typically not effective with more severe cases of xerostomia, nor do they provide long-lasting relief with mild cases.
There are also a number of artificial salivas on the market which contain alcohol, mineral oils, glycerine, and combinations of polyethylene glycols. A number of carboxymethylcellulose-based preparations are on the market as well, including those sold under the marks Orex.RTM. (Young Dental), Xero-Lube.RTM. (Scherer), Mci-Stir.RTM. (Kingswood Laboratories), and Salivart.RTM. (Westport Pharmaceuticals). Many patients find, however, that such preparations are irritating or distasteful, and that their lubricating effect is of relatively short duration.
There has also been some experimentation with parasympathomimetic drugs, i.e., drugs that mimic the action of the parasympathetic nervous system which controls salivation. There have been reported dosage control problems with these drugs, however, as well as significant side effects.
The present invention is premised on the surprising discovery that the oil extracted from the Yerba Santa plant (Eriodictyon californicum; Eriodictyon glutinosum; also known as "consumptive's weed"; "bear's weed" "mountain balm" and "gum plant") is extremely effective in providing long-lasting relief in cases of mild to severe xerostomia, with no unpleasant side effects.
The Yerba Santa plant is an evergreen shrub indigenous to the hills and mountains of California and northern Mexico, and was long used by Indians for a number of purposes. See, e.g., A.R. Hutchens, Indian Herbalogy of North America, Ontario: Merco, 1975, at pp. 317-318. A number of references to the Yerba Santa plant teach its use as an expectorant (e.g., N. Coon, The Dictionary of Useful Plants, Emmaus, Pa.: Rodale Press, 1974)), in treating colds, sore throats, catarrh, stomach aches, vomiting and diarrhea (see A.R. Hutchens, supra), in treating hemorrhoids (D.G. Spoerke, Herbal Medications, Santa Barbara, CA: Woodbridge Press, 1980, at p. 183), in treating diseases of the lung (Los Remedios de la Gente: A Compilation of Traditional New Mexican Herbal Medicines and Their Use, compiled by M. Moore, 1977), and in masking the taste of quinine and other bitter medications (Spoerke, supra; see also G.E. Trease et al., Pharmacognosy, London: Cassell & Colber, 1978, at p. 463)). However, the discovery that Yerba Santa is effective in significantly alleviating xerostomia is novel and completely unsuggested by the art.